Burners having a pulsating mode of operation

ABSTRACT

A BURNER HAVING A PULSATING MODE OF COMBUSTION AND WHICH CAN BE USED TO CARRY OUT FREE RADICAL REACTION COMPRISES (A) A COMBUSTION CHAMBER (PREFERABLY CYLINDRICAL WITH AN ACTUAL LENGTH OF AT LEAST TEN TIMES THE AVERAGE DIAMETER) WHICH HAS GROSSLY ROUGH WALLS, AND (B) AN OXYGEN/FUEL INLET SYSTEM WHICH HAS A LOW RESISTANCE TO GASEOUS FLOW. DURING USE THE CONTINUOUSLY FLOWING FUEL MIXTURE IS PERIODICALLY IGNITED. ONE COMBUSTION WAVE TRAVELS DOWNSTREAM UNTIL THE MIXTURE IS EXHAUSTED AND THE OTHER TRAVELS UP-STREAM UNTIL IT REACHES THE POINT AT WHICH THE FUEL AND OXYGEN INLET SYSTEMS SEPARATE.

July 4, 1972 D. H. DESTY EI'AL 3,674,409

BURNERS HAVING A PULSATING MODE OF OPERATION Filed Aug. 26, 1969 4Sheets-Sheet 2 T 4 g 4 53 "70 E 52 53/ 4V 7* /A/VEAI 702s 05A: HEA/AV0::77/ Ba er Hates/2T flew/a; war/I444 y 1972 D. H. DESTY EI'AL3,674,409

BURNERS HAVING A PULSATING MODE OF OPERATION Filed Aug. 26, 1969 4Sheets-Sheet 4 06AM: H6412? parry 5,4227 MEEa-Fr Fen/v0: MHIMAA Arra VUnited States Patent 3,674,409 BURNERS HAVlNG A PULSATING MODE OFOPERATION Denis Henry Desty, Weybridge, and Barry Herbert FrancisWhyman, Teddington, England, assignors to The British Petroleum CompanyLimited, London, England Filed Aug. 26, 1969, Ser. No. 853,043 Claimspriority, application Great Britain, Sept. 16, 1968, 43,938/ 68 Int. Cl.F23c 3/02 11.5. Cl. 431-1 3 Claims ABSTRACT OF THE DISCLOSURE A burnerhaving a pulsating mode of combustion and which can be used to carry outfree radical reactions comprises (a) a combustion chamber (preferablycylindrical with an actual length of at least ten times the averagediameter) which has grossly rough walls, and (b) an oxygen/fuel inletsystem which has a low resistance to gaseous flow. During use thecontinuously flowing fuel mixture is periodically ignited. Onecombustion wave travels downstream until the mixture is exhausted andthe other travels up-stream until it reaches the point at which the fueland oxygen inlet systems separate.

This invention relates to a burner which has a pulsating mode ofoperation, that is to a burner which burns its fuel in a series ofdiscrete explosion waves and to a method of generating a series ofcombustion explosion waves from a gaseous oxygen/fuel mixture.

Burners which produce a series of explosion waves can be used forgeological formation heating. In addition the pressure pulses can, undercertain circumstances, be used as a replacement for a series of hammerblows.

According to the invention a burner having a pulsating mode of operationcomprises:

(a) a combustion chamber for the period explosive burning of anoxygen/fuel mixture continuously supplied thereto, which chamber has agrossly rough interior wall providing successive pressure wavereflection points for creating secondary ignition centres in advance ofthe combustion wave front of the mixture,

(b) an oxygen/fuel inlet system for continuously supplying an explosiveoxygen/fuel mixture to the com bustion chamber, which system has a lowresistance to gaseous flow and which is arranged to mix the fuel andoxygen at one end of the combustion chamber, and

(c) an ignition source for periodically igniting the continuouslysupplied mixture at the mixing end of the combustion chamber,

whereby, during the use of the burner, a series of explosion waves isproduced by repeated ignition of an explosive mixture formed in thecombustion chamber.

Cylindrical combustion chamber are particularly suitable, especiallythose whose axial length is at least times their average diameter.

The oxygen is supplied to the burner in the gaseous phase and it may besupplied as a gaseous mixture, e.g. air. As stated above the oxygeninlet system must offer a low resistance to the flow of the gaseousoxygen.

The fuel may be liquid in which case the fuel inlet system may take theform of an atomiser for spraying fine droplets of liquid fuel into theoxygen flow on entry to the combustion chamber.

Preferably the fuel is gaseous (or vapourised liquid) in which case thegaseous fuel inlet system must also offer a low resistance to the flowof (gaseous) fuel.

The inlet system may be arranged to admit the oxygen and fuel directlyinto the combustion chamber; this forms 3,674,409 Patented July 4, 1972ice a mixing zone at one end of a cylindrical combustion chamber.Alternatively the oxygen and fuel may first pass into one or more smallantechambers Where mixing occurs before the oxygen and fuel pass intothe combutiou chamber.

During use an ignition source is positioned in the combustion chamber.

The invention will now be described by way of example with respect tothe drawings in which:

FIGS. 1a1e illustrate five stages in the propagation of one combustionwave,

FIGS. 2-4 are longitudinal cross sections showing various inlet systemsand spark plug arrangements, and

FIG. 5 is a cross section on the line 55 of FIG. 4, and

FIG. 6 illustrates a burner with a continuous ignition source.

FIG. la shows a burner which comprises a cylindrical combustion chamber10 just after the ignition spark, the inner wall of the chamber beingmacroscopically rough, that is, sufliciently rough to enable surfaceirregularities to be observed by the unaided eye, for reasons which aremore fully set forth below. At this stage there is in the explosive gasmixture in the chamber, a spherical combustion Wave or flame front 11with a slug of hot burnt gas inside; as the time passes the slug of hotburnt gas grows larger as does its enveloping spherical combustion wavefront and it also moves down-stream with the downwardly moving gas flowbecause the initial flame velocity of the explosive gas mixture is lessthan the velocity of the downwardly moving, incoming gas.

At the stage shown in FIG. 1b the spherical combustion wave front 11 hasgrown until its radius has exceeded that of the combustion chamber 10 soit has divided into two turbulent accelerating combustion wave or flamefronts 12 and 13 which are separated by an expanding, downwardly-movingslug of hot burnt gas; the wave front 12 travels up-stream and the wavefront 13 travels down-stream. Both combustion wave fronts accelerate bya mechanism in which the associated pressure wave, that is, the pressureWave created in the explosive gas mixture in advance of each combustionwave front, is reflected from successive point on the macroscopicallyrough wall thus creating secondary ignition centres in the explosive gasmixture in advance of the combustion wave front. At the stages shown inFIGS. 1c and 1d, the expanding slug of burnt gas has continued itsdownward movement while the combustion wave fronts 12 and 13 continue toaccelerate through the explosive mixture toward the top and bottom,respectively, of the chamber 10. Finally, as shown in FIG. Ie the wavefront 12 reaches the inlet system where there are separate oxygen andfuel systems and the wave front 12 goes out. The chamber 10 thenre-charges with explosive mixture so that the next cycle can start.

The inlet system shown in FIG. 2 joins the combustion chamber 10 at aninlet port 20 and it has an annular configuration with a central fuelpipe 21 surrounded by an air duct 22. Just upstream of the inlet port 20there is a conical baffle 23 which forms an antechamber 24 adjacent toits conical surface. The conical baffle 23 has a flat base 25 which,during use, deflects the fuel flow into the air flow so that mixingbegins in the anti-chamber 24. All the passages are so wide that theresistance to gas flow is low.

The mixture of air and fuel passes from antechamber 23 into thecylindrical combustion chamber 10 where it is ignited by successivesparks from the plug 26.

A spiral 27 of metal rod semicircular in cross-section, is secured tothe inner Wall 10' of the combustion chamber to form therewith a grosslyrough, or macroscopically rough inner surface providing successivepoints for reflection of a pressure or compression wave created in theexplosive gas mixture in advance of a combustion wave front initiated byignition of the mixture, so that the combustion wave initiated by thespark plug 26 accelerates into an explosion wave.

(The burner was 25 cm. long and its inside diameter was 1.4 cm.,ignoring the spiral which was formed of rod 0.2 cm. diameter. The pitchof the spiral was 0.5 cm.)

In the burner shown in FIG. 3 the spark plug 26 is situated centrally atone end of the combustion chamber 10.

The inlet system comprises an air gallery 33 and a fuel gallery 28.These galleries communicate with the combustiou chamber 10 via (12)pairs of air ducts 29 and fuel ducts 30 which meet at right angles onthe inner wall 10' of the combustion chamber. All the ducts have asufficiently wide diameter to provide a low resistance to the flow ofair and fuel so that an explosive mixture is produced in a mixing zoneat the end of the combustion chamber. As can be seen the walls of thecombustion chamber are water cooled through the provision of watergallery 50. Shoulders 51 rectangular in cross-section are secured to theinner walls 10' to form the desired grossly rough or macroscopicallyrough inner surface as aforesaid. As depicted, these extend radiallyinwardly from the wall for equal distances and are spaced axially fromeach other to provide alternating wide and narrow wall portions, thatis, alternating maximum and minimum diameter portions 52 and 53,respectively, of the chamber.

In the burner embodiment depicted in FIG. 3, the combustion chamber 10is 107 cm. long, its maximum internal diameter is 7.6 cm. and itsminimum internal diameter is 6.0 cm. The axial length of each wideportion 52 is 0.8 cm. and the axial length of each narrow portion 53 is0.8 cm. This ensures that the combustion waves accelerate into explosionwaves due to compression wave reflections.

The burner shown in FIGS. 4 and 5 also has its spark plug 26 (withannular electrodes) situated centrally at one end of the combustionchamber as can be seen from FIG. 3 the walls of the combustion chamberare externally water cooled.

The inlet system comprises a fuel pipe 21 and an air pipe 22, bothparallel to the axis of the burner, with radial terminal sections 31 and32, respectively. As can be seen more clearly in FIG. 5 the inlet systemalso comprises an antechamber 24 into which the two terminals sections31 and 32 open tangentially. Thus the fuel and oxygen mix by swirling inthe antechamber 24 and the mixture passes into the inlet end of thecombustion chamber 10.

The size and arrangement of the walls of the combustion chamber are thesame as in FIG. 2 save that the spiral 27 is formed of metal rod whichis circular in cross-section.

The burners will operate provided that sparks occur when the combustionchamber contains sufficient fuel. Preferably the spark rate is adjustedto gas flow rate so that the time between sparks equals the timerequired to burn the previous charge (in practice this time is smallenough to be neglected) plus the time required to re-fill the combustionchamber with fresh mixture. Variations from this setting mean thateither unburnt gas leaves the burner or burning takes place in only aportion of the combustion space. For high flame speed fuel gases, e.g.hydrogen, quite small sparks, e.g. millijoule energy sparks such as areused in automobile practice, are suitable but with fuel gases of lowflame speeds, e.g. methane and natural gas, a spark energy of 2-3 joulesmay be necessary to combat (a) poor mixing in the free flow system and(b)slow flame acceleration.

A burner with a modified ignition source is illustrated in FIG. 6. Ingeneral the burner is as illustrated in the previous figures with themodification of a side arm 40 having a vent 41 adjacent to a hotfilament 42.

Shortly after a detonation the burner will, as described above, be fullof burnt gas and it will be apparent that the side arm 40 will also befull of burnt gas. As the new 4 charge re-fills the burner it will alsoenter the side arm 40 driving the burnt gas through the vent 41. Whenthe new charge reaches the continuously glowing filament 42 ignitionwill occur and the flame will travel along the side arm 40 into theantechamber 24 and thereafter combustion propagation will take place asdescribed above.

The timing of the ignition is controlled by the time taken for the nextmixture to reach the glow wire 42 and, in its turn, this time iscontrolled by the size of the vent 41. Thus more frequent ignitions(i.e. smaller charges) can be achieved by opening the vent 41 to allowquicker access of combustion mixture to the glow filament 42. Similarlyslower ignitions can be achieved by closing the vent 411. It will alsobe apparent that the ignition of full charges will occur when the vent41 is of such a size that the side arm 40 fills in the same time as thecombustion chamber 10.

All the embodiments so far described have required an electric powersource (not shown in any drawing) for ignition. If no electric power isavailable ignition may be achieved by a simple modification of FIG. 6which is not shown in any drawing. In this modification a pilot flame,operated from the fuel/air system, is positioned just outside the vent41 and when fresh mixture exhausts through the vent ignition occurs.

The burners described above have been successfully operated at ambientpressures of up to 30 atmospheres. The following table lists some of thefuel/oxidant mixtures which have been successfully used in a burnerhaving spark plug ignition and an internal diameter of 12 mm.

Pressure Fuel Oxidant rise Hydrogen..

D 0 Town's gas Methane o Propane (commercial). Butane (commercial)Kerosene Air Combustion reactions These use the natural quenching effectbehind a rapidly moving detonation type wave to stabilize certainproducts. For example hydrogen peroxide can be prepared from hydrogen/oxygen mixtures near the oxygen rich limit, where the formation of H 0controls the reaction 0H +OH H 0 In the case of hydrocarbon fuels,aldehydes (i.e. partial combustion products) can be obtained e.g.formaldehyde with methane as the fuel.

Gas phase reactions These are mainly reactions involving free radicals.Any added material must be reasonably stable at high temperatures, e.g.water and haloalkanes (carbon tetrachloride). One possible reaction isthat between ethylene and carbon tetrachloride to produce chlorinatedtelomers and addition compounds, carbon tetrachloride would be added tothe ethylene fuel stream and reaction schemes such as that below wouldlead to the chlorinated products.

Free radicals such as hydroxyl, methyl, methylene (carbene) and hydrogenatoms will come into contact with the wall liquid film and react.

Systems include (i) Homolytic aromatic substitution by alkyl radicalsand hydroxyl (e.g. free radical attack on benzene rings) such as theformation of l-naphthol from naphthalene (ii) Hydration of long chain(e.g. with to 20 carbon atoms) olefines via hydroxyl radicals.

(iii) Insertion and addition reactions of carbenes with aromatic systemsand olefins.

We claim:

1. A burner having a pulsating mode of operation,

which burner comprises:

(a) a combustion chamber for the timed periodic explosive burning ofsuccessive separate charges of an explosive oxygen/fuel mixturecontinuously supplied to said burner, the inner wall of said chamberbeing cylindrical and having a spiral of metal rod secured to the innerwall to form successive pressure wave reflection points extendinggenerally radially inwardly of said chamber from said wall at selectedsuccessive intervals along the length of said chamber, for reflectingpressure waves resulting from burning of each explosive mixture chargeto create secondary ignition centres in the explosive mixture charge inadvance of combustion wave fronts initiated by ignition of the charge;

(b) an oxygen/ fuel inlet system for continuously supplying oxygen andfuel to the burner at one end of the combustion chamber, which systemhas a low resistance to gaseous how and which is arranged to mix thefuel and the oxygen at said one end of the combustion chamber so aswntinuously to provide successive separate explosive mixture charges insaid chamber; and,

(c) an ignition source at said one end of said combustion chamber forinitiating, at selected periodic intervals, ignition of the continuouslyprovided successive separate explosive mixture charges at said one endof said chamber,

whereby, during use of the burner, a series of explosion waves isproduced in said burner by periodic ignition of the successive separateexplosive mixture charges.

2. A burner according to claim 1 in which said spiral is of uniformpitch.

3. A burner having a pulsating mode of operation,

which burner comprises:

(a) a combustion chamber for the timed periodic explosive burning ofsuccessive separate charges of an explosive oxygen/fuel mixturecontinuously supplied to said burner, the inner wall of said chamberhaving a macroscopically rough surface providing successive pressurewave reflection points extending generally radially inwardly of saidchamber from said wall at selected successive intervals along the lengthof said chamber, for reflecting pressure waves resulting from burning ofeach explosive mixture charge to create secondary ignition centres inthe explosive mixture charge in advance of combustion wave frontsinitiated by ignition of the charge;

(b) an oxygen/fuel inlet system for continuously supplying oxygen andfuel to the burner at one end of the combustion chamber, which systemhas a low resistance to gaseous iiow and which is arranged to mix thefuel and the oxygen at said one end of the combustion chamber so ascontinuously to provide successive separate explosive mixture charges insaid chamber, said oxygen/fuel inlet system comprising an ante-chambercommunicating with one end of said combustion chamber, in whichante-chamber the fuel and oxygen are mixed before passing into thecombustion chamber and said system also comprising means forming aninlet port joining said system to said one end of said combustionchamber, a central fuel pipe, an annular air duct surrounding said fuelpipe, and a conical baffle disposed upstream of said inlet port andbeneath said fuel pipe and forming said ante-chamber adjacent to theconical surface of said baffle, said baflle having a flat base fordeflecting fuel flow from said central fuel pipe into the air flow fromsaid annular air duct, so that mixing begins in said ante-chamber; and,

(c) an ignition source at said one end of said combustion chamber forinitiating, at selected periodic intervals, ignition of the continuouslyprovided successive separate explosive mixture charges at said one endof said chamber,

w hereby, during use of the burner, a series of explosion waves isproduced in said burner by periodic ignition of the successive separateexplosive mixture charges.

References Cited UNITED STATES PATENTS 1,381,095 6/1921" Starr 239-404 X1,434,256 10/ 1922 Thompson 43 l1 1,841,169 1/1932 'Butz 431-353 X2,425,975 8/ 1947 Wtitte et al 43 l1 X 2,715,436 8/ 1955 Lafferentz etal 431-1 3,473,879 10/ 196 9- Berberich 4311 3,516,253 6/ 1970 Allportet a1 60--39.77 2,612,749 10/ 1952 Tenney et al 60-249 FOREIGN PATENTS174,726 3/1961 Sweden 431-1 CARROLL B. DORlT Y, JR., Primary ExaminerUS. Cl. X.R. 431-353; 60--39.77 1

